Aeronautical propeller



Dec. 1 1931. s. A. REED 1,833,911

4 AERONAUTICAL PROPELLER Filed Nov. 19. 1929 Pa /(,4 I

INVENTOR BY SYLVANUSAREED.

Patented Dec. 1, 1931 UNITED STATES PATENT OFFICE SYLVANUS A. REED, OF NEW YORK, N. Y., ASSIGNOE TO THE REED PROPELLER 00., INCL,

' .A. CORPORATION OF NEW YORK EERONAUTICAL 'PROIPELLER This invention relates to aeronautical propellers of the solid single piece thin blade metal type and constitutes improvements upon the propellers described in my United States Patents Numbers 1,463,556 and 1,518,410.

One of the objects of my invention is the reduction of weight of propellers without loss of efiiciency and with low cost of production.

A further object is to produce a steel blade propeller of the thin blade metal type which may be lighter than a .conventional light alloy propeller and at the same time to avoid hollow construction involving; the use of structural welds, such welds being especlally objectionable in the region of the blade tips.

A further object is to makeuse of the tandem arrangement of propellers to effect an initial large reduction in weight. By making at each radius the aggregate chord of the tandem elements'substantially equal to the chord of a conventional blade for the desired duty and of the same aerofoil shape in cross section, I greatly reduce the aggregate cross sections at such radii, and hence reduce the total weight.

A further object is the elimination of much metal in the blade roots and at the hub whereby a further important reduction in weight of the propeller is attained without impairment of strength.

Further objects will be apparent from a reading of the subjoined specification and claims and from a consideration of the drawings. 1

In order to explain the invention more clearly, one embodiment thereof is shown in the accompanying drawings. in which:

Fig. 1 is an elevation of a tandem propeller illustrating my invention;

Fig. 2 is a plan View of the propeller shown in Fig. 1;

Fig. 3 is an elevation of one of the blades shown in Fig. 1;

Fig. 4 is a cross section taken on the line 4-4 of Fig. 2;

Fig. 5 is a cross sect-ion taken 55 of Fig. 2;

Fig. 6 is a cross section taken on the line 6-6of Fig. 2;

Fig. 7 is a cross section taken on the line 77 of Fig. 2; and

Fig. 8 is an elevation of the central hub and core member used in assembling the blades of my tandem propeller.

In general, the tandem four blade propeller used for illustration of my invention comprises a pair of propellers united with a core member so that the propellers are arranged in tandem and form in effect a single propeller for the portion thereof which is adjacent to the hub, but two propellers for the portion thereof which ext-ends beyond the core member. Each propeller has two blades and is formed similarly to the propellers disclosed in my United States Patent Number 1,687,636. Each propeller has the camber face of one blade on the side of the blade opposite to that of the camber face of the other blade. The core member extends outward from the centralhub a substantial. distance but less than half the length of each blade and unites the two propellers.

Referring specifically to the drawings, the illustrated propeller is assembled from the two blades (1 and b and united by the central hub and core member 11. Each of these blades is made from a long relatively thin and narrow strip of rolled metal, preferably alloy steel, 1 being one blade of propeller a and 2, the other blade. 3 is the leading edge of blade 1 and 5 the leading edge of blade 2. 4 is the trailing edge-of blade 1 and 6.the trailing edge of blade 2.

The blade faces exposed in Fig. 3 of the drawings are both cambered, andthe reverse faces of both blades are substantiallyfiat. The entire propeller is shown twisted continuously from tip to tip, always in the same on the line angular direction, so that at the center 7 the angle of thefaces to the plane of rotation of the propeller is 90 and the angles of the blade faces at various radii are those appropriate to the desired pitch. In order that, after twisting the cambeg faces should show as in the drawing, it is obvious that, before twisting, they must have been on opposite faces of the untwisted propeller, the con ditions being similar to those referred to in my United States Patent Number 1,687,636. It is also obvious that theleading edge 3 of blade 1 is continued as the leading edge 5 of blade 2. The propeller b is similarly formed.

Each propeller element is first bent edgewise to an ogee, as shown at 8, 9, Fig. 2, and is then bent sidewise to an offset as shown at 10, Fig. 3. It is preferable to make these bends before the blades are twisted to their appropriate pitch.

The two tandem elements having been so formed and bent are then assembled to form a tandem four blade propeller as shown in Figs. 1 and 2, one element being on each side of a central hub and core member shown at 11 in Figs. 1 and 8, and secured thereto by bolts or rivets 12, passing through both tandem elements and the member 11. Member 11 is substantially a solid metal propeller, preferably of forged strong light alloy such as duralumin, with the blades abbreviated, and the central portion is similar in formation and construction to the propeller de scribed in my copending United States patent application Serial Number 93,412. In this core 11, 13 is the hub portion and 14 a shaft pole, and the mounting on the engine,

drive shaft may either be direct, or the hole 14 may have a steel liner with fins or keys as described in my said copending United States patent application Serial Number 93,412.

The preferred form of direct mounting on a splined engine shaft is shown in Fig.

7 in which 15 is a cross section of the core member 11, and 18, 19, are cross sections of the two tandem elements a and b. 16 is a shaft hole splined to fit the splines on the engine shaft (not shown), and 17, 17 are conical recesses to receive the corresponding cone elements of a conventional splined engine shaft.

24 and. 25 are the truncated blades of the .hub or core member 11. The'length of both blades of said core member 11 is preferably about of the total blade length of the propeller and the edges may be faired to the two propellers to improve'the streamline characteristics of tlte composite section as shown in cross section 21 Fig,' 6, taken at 26 of Figs. 1, 2, 3.

I make the cross sections of the two tandem elements at all radii adequate to support the centrifugal stresses with an appropriate factor of safety, say 8 1, butinadequate to support more than partly-the bending and torsional stresses occurring at radii within that of the core member'blades 24 and 25, the supplementary support being suppliedby core member 11. I prefer to incline the holes for the rivets 12, in the elements a and I), in the direction of the blade lengths, that is to say radial, so that core 11 takes no share-in sustaining the centrifugal stresses of blades 1 and 2 of the propeller elements a and b, but sustains only its own centrifugal stresses. As the blades 24 and 25 are short, their centrifugal stresses are very moderate and their cross sections can be very moderate in area, though large in outside dimensions or periphcry, for better resistance to bending and torsion. I therefore may have lightening soles 20 or similar excavations or removals of ma terial to reduce the weight of member 11, without impairing its ability to sustain the stresses it is designed to meet.

I prefer to dispose the blades so that the inner space is not less than the blade width beyond the one half radius, and that the tips may be either in tandem line, or may be moderately staggered, with the forward blade in the rear, as shown at 27 Fig. 4 which is a cross section at 28 of Fig. 2. The numeral 29 in Fig. 5 indicates a cross section at about :4 radius showing the blades more nearly in The bending at 10, Fig. '3 and at 8 and 9,

Fig. 2 is preferably of such character that the axis of the centers of gravity of the blades tandem element a will be continued as the radial line of the opposite blade of the other tandem element b as shown in' Fig. 2 at 22-22 and 231 -23. The blades may t en il iverge in the plane of rotation as shown in It will be noted that bolts or connections 12 pass through from near the trailing edge of one blade to near the leading edge of the adjacent blade. braces the assembled pairs of blades against torsional changes or flutter. I may also have a plurality of similar bolts or attachments. Offsets 31 and 32 are provided in the mass of core member 11 against which the central.

element of the tandem have one blade for-v ward and the other rearward, with an ogee cross-over at the huh, I am able to obtain a symmetrical and balanced tandem assembly,

with the forward blades adequately spaced ahead of the rearward blades, and yet the assembled propellers occupying not more than a moderate space on the hub. I am also able to make a propeller from commercial rolled This greatly fortifies, and

of one element to be a forward blade of the tandem, and the other blade of the same element to be a rear blade of the tandem, and each element sustaining its own centrifugal stresses unaided.

2. A tandem metal aeronautical propeller of four blades comprising two two-blade single piece propeller elements, each carried past a hub or core member, one on each side, and bent edgewise in ogee form to cause one blade of one element to be a forward blade of the tandem, and the other blade of the same element to be a rear blade of the-tandem, and each element sustaining its own centrifugal stresses unaided, the core member having relatively short blades extending between the propeller blades and attached thereto for reinforcing and bracingagainst bending and torsional stresses.

3. A tandem propeller braced against angle change stresses by means located at points within the inner half of the respective blade lengths and connecting thetrailing edge of each forward blade with the leading edge of the adjacent rearward blade.

4. A tandem meta-l aeronautical propeller of four blades comprising two two-blade single piece propeller elements, each carried past a. hub or core member, one on each side, and bent edgewise in ogee form to cause one blade of one element to be a forward blade of the tandem, and the other blade to be'a rear blade of the tandem, each element sustaining its. own centrifugal stresses unaided, and each blade being bent to lie substantially on a radius from the driving axis, with the blade tips in moderately staggered tandem aspect, the forward blade being in the rear of the stagger.

5. A tandem propeller comprising propel-' ler elements made of alloy steel, and a hub and core'member of strong light alloy, having short blade extensions cooperating with the propeller blades in supporting their hen ding and torsional stresses.

6. A tandem metal aeronautical propeller of four blades comprising two two-blade single piece propeller elements, each carriedpast a hub or core member, one on each side, and bent edgewise in ogee form to cause one r blade of one element to be a forward blade of the tandem, and the other blade to be a rear blade of the tandem, each element sustaining its own centrifugal stresses unaided,'and each two blade element being made from a fiat metal strip byforming a camber face on one side of the strip for one blade, and a camber face on the other side of the strip for the other blade, and then twisting always in one angular direction so that both camber faces are brought to the forward side of the propeller. I v

7. A tandem metal aeronautical propeller of four blades comprising two two-blade single piece propeller elements, each carried past a hub or core member, one on each side, and bent edgewise in ogee form to cause one blade of one element to be a forward blade of the tandem, and the other blade to be a rear blade of the tandem, each element sustaining its own centrifugal stresses unaided, the hub or core member being reduced in weight by depressions in its faces, over which the blade elements extend.

8. A metal aeronautical propeller with solid thin blades in which each blade is of the a design of a conventional propeller and is subdivided into sets of several blades in tandem, the aggregate chords of the sets are equal to the chords of the conventional propeller at the same radius, and the profiles and camber ratios of the set are the same in reduced size as that of the conventional propeller at the same radius whereby a weight reduction is effected.

9. A, tandem propeller comprising a core portion having longitudinally extending blades formed with a curved contour; and a pair of propeller elements having a curved contour to conform to the curved contour of the core portion, having relatively thin blades, fastened to the' said core, and positioned on opposite sides thereof.

10. A tandem propeller comprising a core thereof from that of a conventional single piece forged or rolled steel'solid blade thin propeller which comprises forming a pair of single piece two-blade solid thin metal propeller elements, forming a core member with truncated blades of forged strong light alloy, assembling and attachin the two propeller elements one on each si e of the core member, distorting each element to bring one blade of each element into forward position and the other blade into rearward position and to bring the tips in tandem with moderate interspace, and removing metal to the minimum cross section for sustaining centrifugal stresses relying for resistance to other stresses I substantially upon the central core.

In testimony whereof I hereunto aifix my signature.

SYLVANUS A. REED. 

